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FOREST RESEARCH NOTES 

NORTHEASTERN FOREST EXPERIMENT STATION 

f~~EST SER~~CF Upper Darby, Pennsylvania 

0 /GJ rn TM OF AGR\G~~ No* 19554 

Root Competition Slows Growth Of P1anting.s 

On Unprepared Sites In Scrub Oak 

a Planting experiments during the past 7 years on the 

Dilldown Unit of the Delaware-Lehigh Ekperimental Forest in 

Pennsylvania and elsewhere in the scrub oak type have been 

aimed at finding methods for converting the scrub cover to 

more valuable timber types at least cost. Some sort of site 

preparation has been recognized from the beginning as essential to successful planting on much of the scrub oak land. 

Mechanically cleared strips 4 feet or more wide are 

effective but costly. Most tree seedlings planted in such 

strips will get through without benefit of additional release treatment. Killing the brush overall or in strips by 

use of silvicides with ground equipment is even more costly 

JL and poses planting difficulties. " 

In the more open stands of scrub oak, another possibility was considered: interplanting skeleton stands of 200 

to 400 trees per acre without site preparation. A seedling 

in an opening of width equal to or greater than the height 

of the brush might be expected to come through without help. 

Such interplantings were made in 1950 for $12 per acre. 

Survival in this interplanting was satisfactory, but 

by the fourth and fifth years it was becoming increasingly 

apparent that the seedlings were not growing as well as 

where the sites had been prepared. Root competition, particularly from the dense low .ground cover of blueberry and 

sheep laurel, was suspected as the cause of the slower 

growth. To ascertain the reality and magnitude of these 

Jt 

See McQuilkin, W. E. Weed killers of limited use in 

reforesting scrub oak barrens. U.S. Forest Serv.,Northeast. 

Forest Expt. Sta. Forest Res. Note 6. 4 pp. 1951. 

1 

2 
differences associated with site preparation, a srhall study 

was made during the winter of 1954-55. 

Procedure 

Available for comparison were red, jack, and pitch 

pines planted at Dilldown in 1950 from the same lots of 

planting stock under the following conditions: 

1. In bulldozed furrows about L feet wide. 

2. In strips 4 to 5 feet wide which had been treated with 

ammate in 1949. This killed most of the low blueberrysheep laurel ground cover, killed the tops of the scrub 

oak, and retarded development of new basal sprouts fop 2 

years. 

3. In openings between scrub oak clumps, with no site preparation. 

Heights were measured in random samples of 100 trees 

of each species in the furrow plantings and interplantings. 

In the ammate-treated strips (a small test originally), 

there were not 100 survivors of each species. The samples 

here included these numbers of trees: red pine 80, jack pine 

52, and pitch pine 100. 

Results 

Mean heights and their standard deviations were computed, and the differences in height between ground treatments were tested for significance for each species separately by conventional t-test. Heights and standard deviations are shown in the following tabulation. 

Treatment Red pine Jack pine Pitch pine 

Furrowing 2.06+0.61 5.57+1.12 - 4.219.12 

Ammate 1.7953.51 5.6521.42 3.76+0.80 

None (int erplanting) 1.40+0.50 3.355.00 2.419.53 

With one exception--furrowing vs. ammate for jack 

pine--the trees in the furrows average taller than in ammated strips, and trees in both furrows and ammated strips 

average taller than in the interplantings with no site preparation. All these differences within species are significant by the t-test at the 1-percent level; that is, the 
chances are 99 out of 100 that the differences are real 

t reatrrient effects and not random variation. 

Taking the heights in furrol;:s as a base, height 

growth in the interplantings averages 32, 40, and 43 percent 

less for red, jack, and pitch pines respectively. Moreover, 

height does nct tell the shole story. The trees in the furrovlqs have heavier branches and more foliage, and are generally in better vigor. 

Discussion 

Since the trees in these samples were not suffering 

top competition other than some croivding from the sides, the 

height data support the thsorjr that roo$ competition is exertinganimportantinfluenceupongrowth. Best growthin 

the furrows (all root competition remved) , slowest growth 

in the interpiantings (no reduction of competition), and 

intermediate grovith in the awnlted strips (competition partly eliminated) are exactly what might be expected if root 

c~mpetition were the critical factor. 

Whether or not the retarded seedlings in the interplantings will eventually gain the ascendancy and acquire 

normal vigor is not yet known. At present it appears doubtful that many trees will. Therefore extensive interplantings 

without some reduction in the existing root competition cannot now be recommended. A small interplanting experiment involving treatment of the individual planting spots with 

silvicide has recently been begun at Dilldo~vn. This may 

point up a way of coping with the root-competition problem. 

--E. F. McNAM-4RA 

Pennsylvania Department of Forests and Waters 

and 

IRVIN C . REIGNER 

Northeastern Forest Experiment Station 

Forest Service, U.S. Dept. Agriculture 

AGRICULTURE-FOREST SERVICE-UPPER DARBY